Method for manufacturing superconducting patterns

ABSTRACT

A manufacturing method of Josephson devices is described. A superconducting ceramic film is deposited on a non-conductive surface and partly spoiled in order to form a barrier film by which two superconducting regions is separated. The spoiling is performed by adding a spoiling element into the ceramic film by ion implantation.

This application is a Continuation of Ser. No. 07/239,288, filed Sep. 1,1988, now abandoned, which, in turn is a continuation-in-part of Ser.No. 07/176,144, filed Mar. 31, 1988, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a method of manufacturing superconductingpatterns.

Along with efforts to make integrated circuits more dense, highoperational speeds are required. The fine structures of electriccircuits give rise to problems of decrease in operational speed and inreliability at exothermic parts of integrated circuits. Because of this,if semiconductor devices are driven at the boiling point of liquidnitrogen, the mobilities of electron and hole become 3-4 times as fasteras those at room temperature and as a result the frequencycharacteristics can be improved.

The Josephson devices such as a memory which functions based on theJosephson effect are known as superconductive electronical devices. Inthis device, switching operation assciated with the Josephson effect isperformed. A schematic view of an example of such a device is shown inFIG. 1. The device comprising a superconducting film 24 adjoined to asuperconducting region formed within a substrate 21 with a barrier film23 therebetween. The advantege of the device is operability at a veryhigh frequency. However, the oxygen proportion contained in thesuperconducting ceramics of this type tend to be reduced.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method ofeffectively manufacturing superconducting patterns.

It is another object of the present invention to provide a method ofmanufacturing superconducting patterns at high production yield.

In order to accomplish the above and other objects and advantages,non-superconducting regions are formed within ceramic superconductors byadding an element which fuctions to spoil the superconducting structureof the ceramics and insulating the same. The non-superconducting regionis thermal annealed or fired. When a superconducting film is formed on asurface, the ( a, b ) plane in the crystalline film is aligned parallelto the underlying surface because current can flow along that plane 100time as dense as along the normal direction thereto.

Preferred examles of the elements to be added to superconductingceramics for the purpose of converting the superconducting structure toinsulating non-superconducting structure are Si, Ge, B, Ga, P, Ta, Mg,Be, Al, Fe, Co, Ni, Cr, Ti, Mn and Zr. Preferred examles of thesuperconducting ceramic materials used in accordance with the presentinvent i on are represented by the stoichiometric formula, (A_(1-x)B_(x))_(y) Cu_(z) O_(w), where A is one or more elements of Group IIIaof the Priodic Table, e.g., the rare earth elements or lanthanoides, Bis one or more alkaline earth metals, i.e. Ba, Sr and Ca, and x=0-1;y=2.0-4.0, preferably 2.5-3.5; z=1.0-4.0, preferably 1.5-3.5; andw=4.0-10.0, preferably 6.0-8.0. When added to superconducting ceramicsof this type, the spoiled non-superconducting ceramics are representedby the stoichiometric formula, referred to "non-superconductingceramics" hereinafter, [(A'_(p) A"_(1-p))_(1-x) (B'_(q) B"_(1-q))_(x)]_(y) (Cu_(r) X_(1-r))_(z) O_(w), where A' is one or more elements ofGroup IIIa of the Priodic Table, e.g., the rare earth elements orlantanoides, B' is one or more alkaline earth metals, i.e. Ba, Sr andCa, A", B" and X are selected from a group consisting of Mg, Be, Al, Fe,Co, Ni, Cr, Ti, Mn and Zr, and x=0.1-1; y=2.0-4.0, preferably 2.5-3.5;z=1.0-4.0, preferably 1.5-3.5; and w=4.0-10.0, preferably 6.0-8.0. Thenumbers p, q and r are chosen to be 0.99 to 0.80 so that the totalproportion of A", B" and X is 1-25 atom% in the ceramic material,particularly in case of Mg and Al, the proportion may be 1-10 atom %e.g. 5-10 atom %. The total density of the spoiling elements in anon-superconducting ceramic is about 5×10¹⁸ to 6×10²¹ cm⁻³. Since thesuperconducting properties of superconducting ceramics are sensitive toproportion of thier constituents, the spoiling element can be selectedfrom among the constituents of themselves. When superconductingconstituents are employed as the spoiling element, the total density ofthe additional elements is 5×10¹⁹ to 5×10²² cm⁻³.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a prior art superconducting device.

FIGS. 2(A) to 2(C) are cross sectional views showing first, second andthird embodiments in accordance with the present invention.

FIG. 3 is a graphical diagram showing the current voltage characteristicof devices in accordance with the present invention.

FIGS. 4(A) to 4(C) are cross sectional views showing first, second andthird embodiments in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 2(A) to 2(C), superconducting devices in accordancewith the present invention is illustrated.

The device shown in FIG. 2(A) comprises a substrate 1 having anon-conductive upper surface such as a substrate of YSZ(yttriastabilized zircon), a pair of superconducting regions 3 and 5, anintervening barrier film 4 between the regions 3 and 5, insulating films20 positioned at the opposed ends of the superconducting regions 3 and5, an overlying passivation film 11 formed with openings 11-1 and 11-2at the regions 3 and 5 and electrodes 8 and 9 electrically contactingthe superconducting regions 3 and 5.

An examplary method of manufacturing the device will be described.First, a ceramic oxide film of composition in agreement with thecomposition of a superconducting material as specifically stated in thelast portion of this description is formed on the substrate 1 by screenprinting, sputtering, MBE (Molecular Beam Epitaxial), CVD and the othermethods. At the same time or thereafter, the ceramic oxide is thermallyannealed at 600°-950° C. for 5-20 hours followed by gradually cooling.In accordance with experimental, the critical temperature was measuredto be 91K for example.

The barrier film 4 is formed after or before the annealing by adding aspoiling element such as alminium or magnesium by ion implantation to5×10¹⁸ -6×10²¹ cm⁻³, e.g. 2×10²⁰ cm⁻³. This ion implantation isperformed at an accelation voltage of 50-2000 KV with a photoresist maskcovering the superconducting regions 3 and 5 so that the barrier film 4and the insulating films 20 become "non-superconducting." The barrierfilm 4 is no wider than 1000Å in the lateral direction in order topermit tunnel current thereacross.

The passivation film 11 of an insulating ceramic having similarcomposition as the underlying superconducting cramic film is formed overthe structure, followed by oxidation in an oxidizing atmosphere at300°-950° C., e.g. 700° C. for the purpose of fitting the films of thestructure together and compensating the oxygen proportion at the surfacearea. The passivation film 11 is spoiled in the same manner or formed bymaking use of a spoiled composition. The spoiling element is oxidizedduring this oxidation process. Then, after forming the openings 11-1 and11-2, the lead electrodes 8 and 9 is formed in ohmic contact with thesuperconducting regions 3 and 5 respectively. The electrodes 8 and 9 maybe formed of superconducting ceramics. In that case, the formation ofthe electrodes is preferably carried out before the annealing. FIG. 3 isan example of the voltage-current characteristic of the devices inaccordance with the present invention.

In the previous example, the densities of the spoiling elememt in thebarrier film 4 and the insulating films 20 are same. However, byseparately effecting ion mplantation, the films 4 and 20 can be formedso that the density of the barrier film is 0.1 to 20 atom % which is1/10-1/5, e.g. 1/5, of the densityh of the insulating films.

Referring to FIG. 2(B), a second embodiment of the present invention isillustrated. This embodiment is approximately same as the previousembodiment except for a contol electrode 10 formed over the barrier film4 with the insulating film 11 therebetween. The current passing throughthe barrier film 4 is controlled by the applied voltage by the controlelectrode 10. In this embodiment, the barrier film 4 may besuperconducting. In that case, the operation temperature of the deviceshould be selected so that the superconducting barrier film 4 is in anintermediate state between superconducting state and non-superconductingstate. Namely, the temperature is selected within the range from Tconset and Tco. The action of the device is described in our U.S. patentapplication Ser. No. 167,987 filed on Mar. 14, 1988.

Referring to FIG. 2(C), a third embodiment is illustrated. This deviceis approximately same as the second embodiment except for provision ofan underlying control electrode 10'. The barrier film 4 is sandwitchedby the over lying control film 10 and the underlying cotrol film 10'.

FIGS. 4(A) to 4(C) are modifications of the preceding embodiments shownin FIGS. 2(A) to 2(C) respectively. These embodiments are constructed insubstantially same manner with the exception specified as below.

FIG. 4(A) is a cross section view showing a fourth embodiment of thepresent invention. The substrate 1" is a proportion of a siliconsemiconductor substrate within which an integrated circuit is formed.The upper surface of the substrate 1" is made non-conductive by coveringa ceramic oxide film 1'. After forming the superconducting regions 3 and5, the barrier film 4 and the insulating films 20 on the substrate inthe same manner, a superconducting ceramic oxide film 40 is formed andpartly made non-superconducting by adding a spoiling element theretoexcept for connection portions 8' and 9'. Further, a superconductingceramic film 50 is formed on the structure of the film followed byspoiling the superconducting structure except for the electrodes 8 and9. Although the fabricating process substantially corresponds to that ofpreceding embodiments, the electrodes 8 and/or 9 which may be connectedwith the integrated circuit have not to be given thermal treatment at nolower than 400° C. in order to avoid oxidation of the silicon semiconductor by the oxygen content of the superconducting electrodes 8 and9.

Referring to FIG. 4(B), a fifth embodiment of the present invention isillustrated. This embodiment is approximately same as the fourthembodiment except for a contol electrode 10 made of a superconductingceramic formed over the barrier film 4 with the insulating film 11therebetween. The current passing through the barrier film 4 iscontrolled by the applied voltage by the control electrode 10. In thisembodiment, the barrier film 4 may be superconducting. The operationtemperature of the device should be selected so that the superconductingbarrier film 4 is in an intermediate state between superconducting stateand non-superconducting state. Namely, the temperature is selectedwithin the range from Tc onset and Tco.

Referring to FIG. 4(C), a sixth embodiment is illustrated. This deviceis approximately same as the fifth embodiment except for provision of anunderlying control electrode 10'. The barrier film 4 is sandwitched bythe overlying control film 10 and the underlying cotrol film 10'.

Superconducting ceramics for use in accordance with the presentinvention also may be prepared in consistence with the stoichiometricformulae (A_(1-x) B_(x))_(y) Cu_(z) O_(w), where A is one or moreelements of Group IIIa of the Priodic Table, e.g., the rare earthelements, B is one or more elements of Group IIa of the Periodic Table,e.g., the alkaline earth metals including beryllium and magnesium, andx=0-1; y=2.0-4.0, preferably 2.5-3.5; z=1.0-4.0, preferably 1.5-3.5; andw=4.0-10.0, preferably 6.0-8.0. Also, superconducting ceramics for usein accordance with the present invent i on may be prepared consistentwith the stoichiometric formulae (A_(1-x) B_(x))_(y) Cu_(z) O_(w), whereA is one or more elements of Group Vb of the Priodic Table such as Bi,Sb and As, B is one or more elements of Group IIa of the Periodic Table,e.g., the alkaline earth metals including beryllium and magnesium, andx=0.3-1; y=2.0-4.0, preferably 2.5-3.5; z=1.0-4.0, preferably 1.5-3.5;and w=4.0-10.0, preferably 6.0-8.0. Examples of this general formula areBiSrCaCuCu₂ O_(x) and Bi₄ Sr₃ Ca₃ Cu₄ O_(x). Tc onset and Tco samplesconfirmed consistent with the formula Bi₄ Sr_(y) Ca₃ Cu₄ O_(x) (y isaround 1.5) were measured to be 40°-60° K., which is not so high.Relatively high critical temperatuers were obtained with samplesconforming to the stoichiometric formulae Bi₄ Sr₄ Ca₂ Cu₄ O_(x) and Bi₂Sr₃ Ca₂ Cu₂ O_(x). FIGS. 7 and 8 are graphical diagrams showing therelationship between the resistivity and the temperature for bothsamples. The number x denoting the oxygen proportion is 6-10, e.g.around 8.1. Such superconducting materials can be formed by screen pressprinting, vacuum evaporation or CVD.

While a description has been made for several embodiments, the presentinvent i on should be limited only by the appended claims and should notbe limited by the particualr examles. For example, the present invetnioncan be applied for SQUIDs, VLSIs or ULSIs. The superconducting ceramicsin accordance with the present invention may have single crystalline orpolycrystalline structures.

I claim:
 1. A method of producing a superconducting patterncomprising:forming an oxide superconducting film on a surface; havingits C plane parallel to a surface of a substrate in said film; wherein aselected portion of said superconducting film is doped with dopant inorder that the superconductivity in said portion is decreased.
 2. Themethod of claim 1, wherein said oxide superconducting film is separatedinto two parts with said portion therebetween.
 3. The method of claim 2,wherein said doped portion is in the form of a barrier layer and thethickness thereof is thin enough so that a current can passtherethrough.
 4. A method of producing a superconducting patterncomprising:forming an oxide superconducting film on a surface of anon-superconducting substrate having its C plane parallel to saidsurface in said film; wherein a selected portion of said superconductingfilm is doped with dopant in order that the superconductivity in saidportion is decreased and said portion having a decreasedsuperconductivity is utilized as an insulating portion so that saidsuperconducting portion is electrically isolated from adjacentsuperconducting portion.
 5. The method as defined in claim 4, whereinsaid selected portion is doped by ion implantation.
 6. The method asdefined in claim 4, wherein said selected portion is doped by ionimplantation to 5×10¹⁸ -6×10²¹ cm⁻³.
 7. The method as defined in claim4, wherein said dopant is selected from a group including Si, Ge, B, Ga,P, Ta, Mg, Be, Al, Fe, Co, Ni, Cr, Ti, Mn and Zr, and mixtures thereof.8. The method as defined in claim 4, wherein said oxide superconductingfilm is formed of a superconducting ceramic material satisfying astoichrometric formula;

    (A.sub.1-x B.sub.x).sub.y Cu.sub.z O.sub.w

where A is at least one element of Group Vb of the Periodic table, B isat least one element from Group IIa of the periodic table, x=0.3-1.0,y=2.0-4.0, z=1.0-4.0 and w=4.0-10.0.
 9. The method of claim 8, whereinsaid superconducting ceramic material is of a single crystallinestructure.
 10. The method of claim 8, wherein said superconductingceramic material is of a polycrystalline structure.
 11. A method ofproducing a superconducting pattern comprising:forming an oxidesuperconducting film on a surface of a non-superconducting substrate;having its C plane parallel to said surface in said film; wherein aselected portion of said superconducting film is doped with dopant inorder that the superconductivity in said portion is decreased and saidportion having a decreased superconductivity is utilized as a part of adevice so that a superconducting current can be passed therethrough. 12.The method as defined in claim 11, wherein said selected portion isdoped by ion implantation.
 13. The method as defined in claim 11,wherein said selected portion is doped by ion implantation to 5×10¹⁸-6×10²¹ cm⁻³.
 14. The method as defined in claim 11, wherein said dopantis selected from a group including Si, Ge, B, Ga, P, Ta, Mg, Be, Al, Fe,Co, Ni, Cr, Ti, Mn and Zr, and mixtures thereof.
 15. The method asdefined in claim 11, wherein said oxide superconducting film is formedof a superconducting ceramic material satisfying a stoichiometricformula;

    (A.sub.1-x B.sub.x).sub.y Cu.sub.z O.sub.w

where A is at least one element of Group Vb of the Periodic Table, B isat least one element from Group IIa of the Periodic Table, x=0.3-1.0,y=2.0-4.0, z=1.0-4.0 and w=4.0-10.0.
 16. The method of claim 15, whereinsaid superconducting ceramic material is of a single crystallinestructure.
 17. The method of claim 15, wherein said superconductingceramic material is of a polycrystalline structure.
 18. A method ofproducing a superconducting pattern comprising:forming an oxidesuperconducting film on a surface of a non-superconducting substrate;establishing a superconducting structure; wherein a selected portion ofsaid superconducting structure is doped with dopant using ionimplantation method at a concentration of 5×10¹⁸ -6×10²¹ cm₋₃ in orderthat the superconductivity in said portion is decreased; wherein saiddopant is selected from a group including Si, Ge, B, Ga, P, Ta, Mg, Be,Al, Fe, Co, Ni, Cr, Ti, Mn and Zr, and mixtures thereof.
 19. The methodas defined in claim 18, wherein said oxide superconducting film isformed of a superconducting ceramic material satisfying a stoichiometricformula;

    (A.sub.1-x B.sub.x).sub.y Cu.sub.z O.sub.w

where A is at least one element of Group Vb of the Periodic Table, B isat least one element from Group IIa of the Periodic Table, x=0.3-1.0,y=2.0-4.0, z=1.0-4.0 and w=4.0-10.0.
 20. The method of claim 19, whereinsaid superconducting ceramic material is of a single crystallinestructure.
 21. The method of claim 19, wherein said superconductingceramic material is of a polycrystalline structure.